The stability issues are a lot better since the last couple of updates. Your mileage will vary, especially on console, but on PC (with a base-spec recommended CPU), the only crashes I tend to get now are with the Chain Gang Mayhem modifier enabled. This isn’t to downplay stability issues with the game. But I’ve got a lot of hours in Zane, and performance is currently the best its been (for me).
I’ve run a CCC Zane since release, I don’t use Seein’ Dead, and I’ve been comfortably at M4 without thinking too much for some time now. I could probably push it up to M6 with my current gear and not suffer too much.
Don’t get me wrong. I think there’s room to improve Zane, and I think the developers relying on Seein’ Dead is a poor choice that maybe served as a (long-term) stopgap for Zane’s balance issues. But he’s not bad, in fact he’s quite good, and CCC Zane is definitely a unique playstyle in this game. Nobody else relies on Cryo quite like him (especially with that build).
Under Cover is an . . . okay skill tree. I wouldn’t say “worst”, but it has a lot of problems in scaling with endgame (Mayhem), as well as being superceded by specific Guardian perks. The Barrier is great, Brain Freeze is great, dome Barrier is basically required to keep shields up for perma AS triggering through CCC. The capstone is poor though, and the Augments are a bit meh outside of cheesing movement speed (which you can now do with a Mayhem modifier) and my personal favourite - Deterrence Field. Nothing like near-perma stagger on all enemies in contact with the shield. It rewards getting up close and personal, which synergises with high-crit multi-pellet things like Jakobs’ shotguns (thank heavens for the Hellwalker buff).
One of the biggest complaints about the green tree, from memory, was that it’s a bit boring. Very straightfoward interactions outside of Brain Freeze > CCC. Add to this the Guardian perks and even Mayhem modifiers that take away the green tree’s strengths, and you have a tree that might not be bad, but has gotten worse as time has gone on.
I still run Barrier / SNTL myself, but I also don’t push M7+ and don’t need to mess about with clone-swapping Anointments. I’m hoping the fourth skill trees are real, are coming, and come with a general skill rebalance as well. That’s what I’m dreaming of.